Denitrification filter media and water purification equipment

Abstract

To provide a denitrification filter material which keeps its shape without losing its shape and is digested only when denitrification bacteria feed on it. [Solution] The denitrification filter medium of the present invention is composed of a biodegradable melt-kneaded resin composition containing (A) a water-insoluble and / or sea-insoluble, biodegradable resin component and (B) a biomass polysaccharide polymer component. Component (A) is preferably an ester-bonded polymer, more preferably containing one or more selected from polybutylene succinate adipate, polyhydroxyalkanoate, and polycaprolactone. Furthermore, component (B) preferably contains a biomass polysaccharide polymer component with a helical molecular structure. A water purification apparatus includes a denitrification tank to which water to be treated is supplied, the above-mentioned denitrification filter medium contained in the denitrification tank and adapted to establish aerobic denitrifying bacteria that reduce nitrate nitrogen in the water to be treated, and an air supply mechanism for supplying air to the water to be treated.

Description

Technical Field

[0001] The present invention relates to a denitrification filter medium and a water purification device.

Background Art

[0002] Denitrification devices are widely used in the cultivation of aquatic organisms and in wastewater treatment sites.

[0003] A denitrification device includes a denitrification tank and a denitrification filter medium housed in the denitrification tank and colonized with denitrifying bacteria, and reduces nitrate nitrogen and nitrite nitrogen contained in the water supplied to the denitrification tank by the denitrifying bacteria colonized on the denitrification filter medium under aerobic conditions. As the denitrification filter medium, porous cellulose such as granular, block-shaped, and layered forms is widely used. Since cellulose serves as food for denitrifying bacteria, the number of denitrifying bacteria can increase, and the denitrification ability can be improved.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, in the invention described in Patent Document 1, when attempting to put cellulose at a high concentration, the shape of the denitrification filter medium collapses, and although the denitrifying bacteria are not using it as food, the pulverized cellulose diffuses into the treated water, resulting in potential fouling of the treated water. Therefore, it is necessary to adjust the supply amount of the denitrification filter medium, but this increases the supply frequency of the denitrification filter medium and the burden on the administrator of the denitrification device.

[0006] In addition, bacteria can penetrate to the inside of the cellulose mass, and since the inside of the mass becomes strongly anaerobic, sulfate-reducing bacteria rather than aerobic denitrifying bacteria become dominant, raising concerns about the risk of hydrogen sulfide generation.

[0007] This invention has been made in view of these problems, and aims to provide a denitrification filter material that maintains its shape without being damaged and is digested only when used as food by denitrifying bacteria. [Means for solving the problem]

[0008] The inventors of the present invention have diligently studied to solve the above problems and have found that by using a biodegradable melt-kneaded resin composition containing a resin component that is non-water-soluble and / or non-water-soluble as a denitrification filter material, the collapse of the shape of the denitrification filter material can be prevented, and by making the resin component biodegradable, complete digestion by denitrifying bacteria can be enabled, thereby achieving the above problems and completing the present invention. Specifically, the present invention provides the following.

[0009] The invention relating to the first feature provides a denitrification filter material comprising a biodegradable melt-kneaded resin composition containing (A) a resin component that is water-insoluble and / or water-insoluble and biodegradable, and (B) a biomass polysaccharide polymer component.

[0010] According to the invention relating to the first feature, since the denitrification filter material is a biodegradable melt-kneaded resin composition containing a resin component that is non-water-soluble and / or non-sea-water-soluble, the biomass polysaccharide polymer component contained in the denitrification filter material can be solidified with the resin component, and the shape of the denitrification filter material does not collapse until it is consumed by denitrifying bacteria. In addition, unlike when the resin component is water-soluble, it does not foam in the aquarium. Furthermore, since the resin component is biodegradable, it can be completely digested by denitrifying bacteria, and the water quality is not contaminated by the resin component.

[0011] Furthermore, biodegradation begins preferentially in the biomass polysaccharide polymer components on the surface of the molten-mixed resin composition and inside the voids, maintaining aerobic conditions even inside the molten composition. This allows aerobic denitrifying bacteria to become dominant over sulfate-reducing bacteria, thus reducing the risk of hydrogen sulfide generation.

[0012] Therefore, according to the invention relating to the first feature, it is possible to provide a denitrification filter material that maintains its shape without being disturbed and is digested only when denitrifying bacteria use it as food.

[0013] The invention relating to the second feature is the invention relating to the first feature, wherein the component (A) is an ester-bonded polymer, and provides a denitrification filter material.

[0014] According to the invention relating to the second feature, even if the resin component is water-insoluble and / or non-water-soluble, it is broken down into harmless and non-toxic compounds by simple hydrolysis of the ester main chain within the body of denitrifying bacteria. Therefore, it is possible to achieve both the maintenance of the shape of the denitrification filter media until the denitrifying bacteria feed on the biomass polysaccharide polymer component, and the prevention of water pollution caused by the resin component.

[0015] The invention relating to the third feature provides a denitrification filter material relating to the first feature, wherein component (A) comprises one or more selected from polybutylene succinate adipate, polyhydroxyalkanoate, and polycaprolactone.

[0016] When used for the cultivation of marine organisms, the treated water supplied to the denitrification system is seawater. In this case, component (A) must be marine biodegradable. According to the invention relating to the third feature, since component (A) is marine biodegradable, it can also be applied to the cultivation of marine organisms.

[0017] The invention relating to the fourth feature is the invention relating to the first feature, wherein component (B) contains a biomass polysaccharide polymer component having a helical molecular structure, and provides a denitrification filter material.

[0018] According to the invention relating to the fourth feature, it is possible to include it in the composition in a relatively high proportion compared to other biomass components, i.e., biomass components that do not have a helical molecular structure, and to increase the concentration of feed components. As a result, the frequency of supplying denitrification filter media can be reduced, and the burden on the manager of the denitrification equipment can be reduced.

[0019] The invention according to the fifth feature provides a water purification device including a denitrification tank to which treated water is supplied, the denitrification filter medium according to the inventions of the first to fourth features that is accommodated in the denitrification tank and on which aerobic denitrifying bacteria that reduce nitrate nitrogen in the treated water are fixed, and an air supply mechanism that supplies air to the treated water.

Effects of the Invention

[0020] According to the present invention, it is possible to provide a denitrification filter medium that maintains the shape of the denitrification filter medium without being broken and is digested only when used as food by denitrifying bacteria.

Embodiments for Carrying Out the Invention

[0021] Hereinafter, specific embodiments of the present invention will be described in detail. However, the present invention is not limited to the following embodiments, and can be implemented with appropriate modifications within the scope of the object of the present invention.

[0022] <Denitrification filter medium> The denitrification filter medium is composed of a biodegradable melt-kneaded resin composition containing (A) a resin component that is water-insoluble and / or non-seawater-soluble and has biodegradability, and (B) a biomass polysaccharide polymer component.

[0023] [(A) Resin component that is water-insoluble and / or non-seawater-soluble and has biodegradability] (A) The biodegradable resin component is not particularly limited as long as it is a resin that is water-insoluble and / or non-seawater-soluble and has biodegradability.

[0024] Biodegradability means that microorganisms consume the hydrolyzate hydrolyzed by enzymes contained in certain microorganisms as food and decompose the resin into water and carbon dioxide gas. The component (A) of the present invention is a resin that is insoluble in water and / or seawater as the resin itself and is biodegradable by microorganisms living in water and / or seawater.

[0025] Among biodegradable resins, those using biomass as raw materials include polylactic acid, polycaprolactone, polyhydroxyalkanoate (microbially produced polyester), polybutylene succinate, polybutylene succinate adipate, polyglycolic acid, casein, and low-degree substituted polysaccharide derivatives (such as low-degree substituted cellulose acetate).

[0026] (A) The component is preferably an ester bond polymer. Even if the resin component is water-insoluble and / or non-seawater-soluble, it is decomposed into harmless and non-toxic compounds by simple hydrolysis of the ester main chain in the body of denitrifying bacteria. Therefore, until the denitrifying bacteria consume the biomass polysaccharide polymer component, the shape of the denitrification filter medium does not collapse, and the problem of preventing water pollution caused by the resin component can be achieved simultaneously.

[0027] Polyvinyl alcohols may be classified as biodegradable. However, polyvinyl alcohols are water-soluble and / or seawater-soluble and dissolve in water or seawater to cause foaming, so they are not preferred in the present invention.

[0028] When used for aquaculture of marine organisms, the treated water supplied to the denitrification device is seawater. In this case, (A) the biodegradable resin component is required to have marine biodegradability. Examples of marine biodegradable resins include polyhydroxyalkanoate, polybutylene succinate adipate, and polycaprolactone. Polyhydroxyalkanoate refers to a polymer containing hydroxyalkanoate (hydroxyalkanoic acid) as a monomer component.

[0029] Specific examples of polyhydroxyalkanoates (PHAs) include one or more selected from the group consisting of poly(3-hydroxybutyrate) (PHB), poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), poly(3-hydroxybutyrate-co-3-hydroxyvalerate-co-3-hydroxyhexanoate) (PHBVH), poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBH), and poly(3-hydroxybutyrate-co-4-hydroxybutyrate) (PHBB).

[0030] Other resins that can be decomposed by marine microorganisms include PCL (polycaprolactone) and PBSA (polybutylene succinate adipate). PBSA is a polymer in which 1,4-butanediol is esterified with succinic acid and adipic acid. PCL is a polymer obtained by ring-opening polymerization of petroleum-derived ε-caprolactone. PHA, PBSA, and PCL all have molecular structures in which monomers are linked by ester bonds.

[0031] [(B) Biomass polysaccharide high molecular weight components] (B) Component functions as a plant-derived filler and acts as a filler. Biomass components refer to resources derived from living organisms, and include resources obtained from various sources such as thinned wood from forests, livestock waste, and food waste.

[0032] The biomass component used as component (B) preferably has a helical molecular structure. Examples of biomass components having a helical molecular structure include starch and / or modified starch. When component (B) has a helical molecular structure, it can be included in the composition in a relatively higher proportion compared to biomass components that do not have a helical molecular structure, thereby increasing the proportion of biomass components and allowing for a higher concentration of feed components. As a result, the frequency of supplying denitrification filter media can be reduced, and the burden on the manager of the denitrification equipment can be lessened.

[0033] While biomass polysaccharide polymer components that do not possess a helical molecular structure, such as cellulose, can be used as plant-derived fillers, there are limitations when increasing the proportion of biomass components and reducing the content of biodegradable resins during mixing. However, even in these cases, the coexistence of starch, which has a helical molecular structure, enables mixing at high concentrations.

[0034] Of the starch, 20-25% is amylose and 75-80% is amylopectin.

[0035] Amylose has a structure in which numerous α-glucose molecules are dehydrated and condensed between the hydroxyl groups (-OH) at positions 1 and 4, similar to maltose (α-1,4-glycosidic bond). Because this structure has a bent, maltose-like linkage, it actually has a linear helical structure. The -OH groups within the molecule are used for intramolecular hydrogen bonding, which reinforces the helical structure. In the linear polymerized portion of α-glucose molecules, hydrogen bonds form a helical structure of approximately one turn with 6 α-glucose residues. Furthermore, these helical structures are aligned parallel to each other via hydrogen bonds, forming a crystalline structure. The molecule can form crystals in both a double helix and a single helix state. First, double-helix crystals can be classified into three types: type A, where hydrogen bonds are directly formed between the hydroxyl groups on the glucose residues of each double helix (found in grains such as cornstarch); type B, where a layer of water molecules is sandwiched between them (found in roots and bulbs such as potatoes); and type C, a mixture of both (found in root-derived crystals). Single-helix crystals are called type V and exist naturally as inclusion complexes, where the lipid components contained in starch granules are encapsulated within the amylose single helix.

[0036] Amylopectin has a structure in which numerous α-glucose molecules are dehydrated and condensed between the -OH groups at positions 1 and 4, and between the -OH groups at positions 1 and 6 (α-1,4-glycosidic bonds, α-1,6-glycosidic bonds). Because of the presence of 1,4 and 1,6 bonds, it has a branched helical structure, unlike amylose.

[0037] Cellulose is a linear polymer composed of D-glucose molecules linked by β-1,4-glycosidic bonds. These bonds are very strong, and specific enzymes (cellulases) are required for their decomposition. In contrast, starch is a branched polymer composed of D-glucose molecules linked by α-1,4- and α-1,6-glycosidic bonds. This structure is relatively flexible, and many organisms can produce the enzyme (amylase) that breaks down starch. Therefore, it is presumed that starch is more easily biodegraded by microorganisms, i.e., hydrolyzed by enzymes and its decomposition residues are more readily metabolized into edible substances, compared to cellulose.

[0038] The starch may be classified as waste biomass, underutilized biomass, or resource grain. Furthermore, the biomass material may be of animal origin, such as eggshells.

[0039] The origin of the starch is not particularly limited, but it may be derived from cassava, corn, potato, sweet potato, sago, tapioca, sorghum, beans, bracken, lotus, water chestnut, wheat, rice, oats, arrowroot, peas, etc. Specifically, it may be starch derived from corn or potato, and may also be starch derived from high-amylose corn or potato. One type of starch or a combination of two or more types may be used. Furthermore, the starch may also contain modified starch, such as hydroxypropyl starch, etherified starch, esterified starch, cationized starch, or cross-linked starch.

[0040] The starch in question may be a commercially available product, such as ST Starch P (Nippon Denko Kagaku Co., Ltd.). Other processed starches that have undergone chemical, physical, or biological treatment can also be used.

[0041] The average particle size of the primary particles of component (B) is preferably 50 μm or less, more preferably 40 μm or less, and even more preferably 30 μm or less. If the average particle size of component (B) is large, the surface area of ​​the denitrification filter material is small, which does not function effectively as food for denitrifying bacteria and may affect the denitrification capacity of the denitrifying bacteria, so this is undesirable. The lower limit of the average particle size is not particularly limited, but considering operability, it is preferably 5 μm or more, more preferably 10 μm or more, and even more preferably 15 μm or more.

[0042] In this invention, the average particle diameter of the primary particles of component (B) is measured by photographic imaging. Specifically, the short axis diameter and long axis diameter of each primary particle of component (B) are measured using image analysis software from a magnified image obtained by a transmission electron microscope (TEM) of an electron-stained molded body sample, and the average is taken as the primary particle diameter of that component (B). Next, the volume of each component (B) is approximated by a sphere with the calculated primary particle diameter, and the volume-averaged particle diameter is taken as the average primary particle diameter.

[0043] [(A) component and (B) component ratio] The lower limit of the content of component (B) is not particularly limited, as long as it is within a range that allows for both sufficient strength to be obtained for use as a denitrification filter material and cost reduction. Preferably, the lower limit of the content of component (B) is 100 parts by mass or more per 100 parts by mass of component (A). Furthermore, considering the denitrification effect, the upper limit of the content of component (B) is more preferably 150 parts by mass or more, and particularly preferably 200 parts by mass or more, per 100 parts by mass of resin component (A).

[0044] (B) The upper limit of the content of component (B) is preferably 700 parts by mass or less, more preferably 550 parts by mass or less, and even more preferably 400 parts by mass or less, per 100 parts by mass of resin component (A), from the viewpoint of whether melt mixing is possible.

[0045] [Additives] The biodegradable resin composition in this embodiment may contain various additives, as long as they do not hinder the effects described in this embodiment. For example, additives such as lubricants, crystallization nucleating agents, plasticizers, hydrolysis inhibitors, antioxidants, mold release agents, UV absorbers, dyes, pigments and other colorants, and inorganic fillers can be used as needed, but it is preferable that these additives are derived from biomass.

[0046] [Lubricant] The type of lubricant is not particularly limited. Examples include hydrogenated vegetable oils and fats, fatty acid amides such as behenamide, stearamide, erucamide, and oleamide, alkylene fatty acid amides such as methylenebisstearate and ethylenebisstearate, polyethylene wax, oxidized polyester wax, glycerin monofatty acid esters such as glycerin monostearate, glycerin monobehenate, and glycerin monolaurate, organic acid monoglycerides such as succinic saturated fatty acid monoglyceride, sorbitan fatty acid esters such as sorbitan behenate, sorbitan stearate, and sorbitan laurate, polyglycerin fatty acid esters such as diglycerin stearate, diglycerin laurate, tetraglycerin stearate, tetraglycerin laurate, decaglycerin stearate, and decaglycerin laurate, and higher alcohol fatty acid esters such as stearyl stearate. These may be used individually or in combination of two or more.

[0047] [Crystallization nucleating agent] The type of crystallization nucleating agent is not particularly limited as long as it can promote the crystallization of (A) the resin component. For example, inorganic substances such as boron nitride, titanium dioxide, talc, layered silicates, calcium carbonate, sodium chloride, and metal phosphates; naturally derived sugar alcohol compounds such as erythritol, galactitol, mannitol, and arabitol; and pentaerythritol, polyvinyl alcohol, chitin, chitosan, polyethylene oxide, aliphatic carboxylic acid amides, aliphatic carboxylic acid salts, aliphatic alcohols, aliphatic carboxylic acid esters, dimethyl adipate, dibutyl adipate, diisodecyl adipate, and dibutyl sebacate. Examples include dicarboxylic acid derivatives, cyclic compounds having a C=O and a functional group selected from NH, S, and O within the molecule, such as indigo, quinacridone, and quinacridone magenta, sorbitol derivatives such as sorbitol, bisbenzylidene sorbitol, and bis(p-methylbenzylidene) sorbitol, compounds containing nitrogen-containing heteroaromatic nuclei such as pyridine, triazine, and imidazole, phosphate ester compounds, bisamides of higher fatty acids and metal salts of higher fatty acids, branched polylactic acid, and low molecular weight poly-3-hydroxybutyric acid. These may be used individually or in combination of two or more.

[0048] [Plasticizer] The type of plasticizer is not particularly limited. Examples include modified glycerin compounds such as glycerin, glycerin diacetomonolaurate, glycerin diacetomonocaprylate, and glycerin diacetomonodecanoate; adipate ester compounds such as diethylhexyl adipate, dioctyl adipate, and diisononyl adipate; polyether ester compounds such as polyethylene glycol dibenzoate, polyethylene glycol dicaprylate, and polyethylene glycol diisostearate; benzoate ester compounds such as benzyl 2(2-methoxyethoxy)ethyl adipate; epoxidized soybean oil; epoxidized fatty acid 2-ethylhexyl; and sebaciate monoesters. These may be used individually or in combination of two or more.

[0049] [Method for manufacturing denitrification filter material] The denitrification filter media is composed of a biodegradable molten resin composition. Because the denitrification filter media is made of a biodegradable molten resin composition containing resin components that are non-water-soluble and / or non-water-soluble, the biomass polysaccharide polymer components contained in the denitrification filter media can be solidified with the resin components, and the shape of the denitrification filter media does not collapse until it is consumed by denitrifying bacteria. In addition, unlike when the resin components are water-soluble, it does not foam in the aquarium. Furthermore, because the resin components are biodegradable, they can be completely digested by denitrifying bacteria, and the water quality is not contaminated by the resin components.

[0050] Furthermore, the biomass polysaccharide polymer components on the surface of the molten-mixed resin composition or inside the voids preferentially begin biodegradation, maintaining aerobic conditions even inside the molten-mixed resin composition. This allows aerobic denitrifying bacteria to become dominant over sulfate-reducing bacteria, thereby reducing the risk of hydrogen sulfide generation.

[0051] The method for manufacturing the denitrification filter material is not particularly limited; for example, a pellet can be produced by dispersing component (B) at a high concentration in component (A).

[0052] <Water purification system> The configuration of the water purification device is not particularly limited, and it is sufficient if it comprises a denitrification tank to which the water to be treated is supplied, the aforementioned denitrification filter material housed in the denitrification tank and for which aerobic denitrification bacteria that reduce nitrate nitrogen in the water to be treated are established, and an air supply mechanism that supplies air to the water to be treated.

[0053] In the water purification device 100 configured as described above, it is preferable that the denitrification filter media 61 and / or nitrification filter media 62 are designed to be less prone to flow even when affected by air bubbles 7. For example, if the denitrification filter media 61 is made less prone to flow and the denitrification reaction is carried out using air bubbles 7, the denitrification filter media 61 is fixed, which allows for the continuous attachment of microorganisms and enables a stable denitrification reaction over a long period of time. Since microorganisms can easily settle on the surface of the denitrification filter media 61, the formation of a biofilm is promoted, creating an environment where denitrifying bacteria can easily live. Furthermore, the risk of wear and damage is reduced because the denitrification filter media 61 does not move, and the lifespan of the denitrification filter media 61 is extended. The same applies to the nitrification filter media 62.

[0054] Specific methods for preventing flow include, for example, housing the denitrification filter material 61 (nitrification filter material 62) in a mesh or net-like container or fixing structure, and ensuring appropriate openings or gaps to control buoyancy caused by bubbles 7. Alternatively, the specific gravity of the denitrification filter material 61 (nitrification filter material 62) itself can be adjusted to resist buoyancy. Furthermore, it is possible to install partitions or dividers to prevent bubbles 7 from directly contacting the denitrification filter material 61 (nitrification filter material 62) and causing turbulence, while promoting the denitrification reaction (nitrification reaction) with a gentle water flow. By combining these methods, it is possible to achieve sufficient contact with bubbles 7 even when the denitrification filter material 61 (nitrification filter material 62) is in a state where it is difficult to flow, thereby achieving efficient and stable denitrification (nitrification) treatment. [Examples]

[0055] The present invention will be specifically described below with reference to test examples, but the present invention is not limited to these. There isn't one.

[0056] [Table 1]

[0057] <Manufacturing of denitrification filter media> (A) The resin component and (B) the biomass component were pre-dried in a hot air dryer (80-100°C, 12 hours), and the moisture content was checked and adjusted during weighing. Then, they were thoroughly mixed in a poly bag in the proportions of (A) and (B) shown in Table 1. After that, the mixture was extruded and cut using a twin-screw extruder (PCM30, manufactured by Ikegai Co., Ltd.) at a set temperature of 180°C and a rotation speed of 100 rpm to obtain kneaded composition pellets.

[0058] The ingredients are as follows: (A) Ingredients: Polybutylene succinate adipate (Product name: BioPBS / FD92PM, Mitsubishi Chemical Corporation) (B) Ingredients: Potato starch (Product name: ST Starch P, Nippon Starch Chemical Co., Ltd., primary average particle size approximately 35 μm) Cellulose (Comparative Example 1, average fiber length 45 μm, average fiber thickness 35 μm) Cellulose (Comparative Example 2, Product Name: Viscoparl P, Rengo Co., Ltd.)

[0059] [Evaluation] Flounder rearing experiment A 150L biological filter tank was installed in a 500L tank of rearing water, and flounder were reared at a stocking density of 1%. During this process, the change in nitrate nitrogen concentration was measured, and the denitrification capacity was calculated.

[0060] In this invention, the denitrification capacity is determined as follows.

[0061] Aquarium water samples were collected every 24 hours, and the nitrate nitrogen concentration in the water was measured. This was repeated for three days. The average of the measurement results was then defined as the denitrification capacity. The nitrate nitrogen concentration was measured using the cadmium reduction method, and in this test, a portable water quality spectrophotometer DR900 (manufactured by HACH) was used.

[0062] Measurement of nitrate nitrogen concentration revealed that Example 1 had a denitrification capacity of 300 mg / L / day. This means that 1 L of denitrification material can decompose and remove 300 mg of nitrate nitrogen per day. Example 2 had a denitrification capacity of 270 mg / L / day, and Example 3 had a denitrification capacity of 200 mg / L / day.

[0063] Cellulose is a linear polymer composed of D-glucose molecules linked by β-1,4-glycosidic bonds. These bonds are very strong, and specific enzymes (cellulases) are required for their decomposition. In contrast, starch is a branched polymer composed of D-glucose molecules linked by α-1,4- and α-1,6-glycosidic bonds. This structure is relatively flexible, and many organisms can produce enzymes (amylases) that break down starch. Therefore, it is thought that in Examples 1 and 2, biodegradation by microorganisms, i.e., enzymatic hydrolysis and the edible metabolism of the decomposition residue, proceeded more easily than in Example 3.

[0064] Furthermore, in all of Examples 1-3, no foaming was observed in the water tank.

[0065] In closed-loop aquarium systems, a protein skimmer (foam separator) is often used in conjunction with the system. This device separates waste products from the water by using foam to raise them to the surface, but if too much foam is produced, it can cause problems by releasing a large amount of aquarium water into the tank. Therefore, traditionally, it was necessary to turn off the protein skimmer after adding denitrifying agents.

[0066] Examples 1-3 are preferable because, since there is no foaming, the protein skimmer can be kept ON even after the denitrification agent has been added.

[0067] On the other hand, in Comparative Example 1, not only was the denitrification capacity limited to 150 mg / L / day, but severe foaming was also observed in the tank. The severe foaming in the tank is presumed to be due to the water-soluble nature of polyvinyl alcohol as a resin component. In Comparative Example 1, as with conventional methods, it was necessary to turn off the protein skimmer after adding the denitrification agent.

[0068] Furthermore, a large amount of bubbles on the water's surface makes it difficult to see underwater, which can interfere with camera monitoring.

[0069] In addition, in Comparative Example 1, jelly-like clumps formed and adhered to multiple locations within the device, resulting in an unsightly appearance. This is presumed to be due to a reaction between PVA and some component, such as oil, contained in the feed, which formed the jelly-like clumps.

[0070] Furthermore, in Comparative Example 2, not only was the denitrification capacity limited to 150 mg / L / day, but foaming was also observed in the tank, requiring the protein skimmer to be turned off after adding the denitrifying material, as in the conventional method. This is presumed to be because the shape of the denitrifying filter media collapsed, causing the pulverized cellulose to diffuse into the treated water even though the denitrifying bacteria were not using it as food, resulting in the treated water becoming contaminated.

Claims

1. Equipped with a breeding tank and a water purification system, The aforementioned water purification device is A denitrification tank to which the water to be treated is supplied, The denitrification filter media housed in the denitrification tank is used to colonize aerobic denitrifying bacteria that reduce nitrate nitrogen in the water to be treated, An air supply mechanism that supplies air to the water to be treated, Equipped with, The aforementioned denitrification filter material is It is composed of a biodegradable melt-kneaded resin composition containing (A) a resin component that is non-water-soluble and / or non-water-soluble and biodegradable, and (B) a biomass polysaccharide polymer component. The aforementioned component (B) contains a biomass polysaccharide polymer component with a helical molecular structure, A closed-circulation aquatic organism rearing system, wherein the content of component (B) is 150 parts by mass or more and 700 parts by mass or less per 100 parts by mass of component (A).

2. The closed-circulation aquatic organism rearing system according to claim 1, further comprising a protein skimmer.

3. The closed-circulation aquatic organism rearing system according to claim 1, wherein component (A) is an ester-bonded polymer.

4. The aforementioned component (A) comprises one or more selected from polybutylene succinate adipate, polyhydroxyalkanoate, and polycaprolactone. The water to be treated is seawater, The closed-circulation aquatic organism rearing system according to claim 1, wherein the target organism to be reared in the rearing tank is a marine organism, and the system is used for the cultivation of marine organisms.

5. The closed-circulation aquatic organism rearing system according to claim 1, wherein component (B) is a combination of a biomass polysaccharide polymer component that does not have a helical molecular structure and a biomass polysaccharide polymer component that has a helical molecular structure.

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